1. Field of the invention.
The present invention relates to a magnetic recording medium having a high coercive force and a method of manufacturing the medium. The magnetic recording medium in accordance with the present invention is suitably used for hard disks, floppy disks, magnetic tape, and other applications.
2. Description of the related art.
In a conventional magnetic recording medium and method of manufacturing the medium, there is known a technique which follows.
FIG. 11 schematically shows an example of a magnetic recording medium for explaining a hard disk. In the drawing, FIG. 11(a) is a perspective view of an entire magnetic recording medium and FIG. 11(b) is a cross-sectional view of a part of the medium of FIG. 11(a) taken along line A-A'.
A substrate body 1 is made up of an Al substrate body 2 and a non-magnetic (Ni-P) layer 3 formed on the Al substrate body 2. Formed on the substrate body 1 are a Cr base layer 4, a ferromagnetic metallic layer 5, and a protective layer 6.
The non-magnetic (Ni-P) layer 3 is formed by a plating or sputtering process on the Al substrate body 2 having a disk shape having a diameter of 89 mm (3.5 inches) and a thickness of 1.27 mm (50 mil) to form a part of the substrate body 1. The non-magnetic (Ni-P) layer 3 is formed thereon with concentric circular scars (which will be referred to as texture hereinafter) by a mechanical polishing process. In general, the non-magnetic (Ni-P) layer 3 has a surface roughness, that is, an average roughness factor when measured in its radial direction, of 5 to 15 nm. Further, the Cr base layer 4 and ferromagnetic metallic layer 5 (usually, Co alloy magnetic film) are formed on the substrate body 1 by a sputtering process, and finally the protective layer 6 made of carbon, or the like, for protecting a surface of the ferromagnetic metallic layer 5 is provided on the layer 5 by a sputtering process. With respect to the respective layers, the non-magnetic (Ni-P) layer 3 has a typical thickness of 5 to 15 m, the Cr base layer 4 has a typical thickness of 50 to 150 nm, the ferromagnetic metallic layer 5 has a typical thickness of 30 nm to 100 nm, and the protective layer 6 has a typical thickness of 20 to 50 nm.
The prior art magnetic recording medium having the aforementioned layer structure was manufactured under conditions of vacuum pressure in a film formation chamber of 10.sup.-7 Torr before formation of the sputtered film and an impurity concentration in an Ar gas used for the film formation of 1 ppm or more.
When it is desired to fabricate a magnetic recording medium having a high coercive force with use of the aforementioned fabrication method, there has been widely used such a technique that Pt elements are contained in a Co alloy magnetic film as the ferromagnetic metallic layer. The Co alloy magnetic film containing Pt elements is advantageous in that the film can easily be manufactured stably on a mass production basis into media having a high coercive force but also disadvantageous in that the film has problems which follow when compared with a Co alloy magnetic film not containing Pt elements, e.g., a CoCrTa film.
(1) The film is high in fabrication costs. PA1 (2) The film is high in media noise of electromagnetic conversion characteristics and thus tends to have a low signal-to-noise ratio.
In order to solve such problems, there is disclosed such a technique as disclosed in an International Patent Application PCT/JP94/01184 Publication. Disclosed in the Publication are high-density recording medium which can increase a coercive force without using an expensive ferromagnetic metallic layer as well as a method of manufacturing the medium. Also disclosed in the Publication is a technique wherein, in the magnetic recording medium using magnetic inversion which comprises of such a medium.